Method for producing noble metal nanocomposites

ABSTRACT

The method for producing noble metal nanocomposites involves reducing noble metal ions (Ag, Au and Pt) on graphene oxide (GO) or carbon nanotubes (CNT) by using  Artocarpus  integer leaves extract as a reducing agent. As synthesized MNPs/GO and MNPs/CNT composites have been characterized using X-ray diffraction (XRD), transmission electron microscope (TEM) imaging, and energy dispersive X-ray spectroscopy (EDX). The TEM images of prepared materials showed that the nanocomposites were 1-30 nm in size with spherical nanoparticles embedded on the surface of GO and CNT. This synthetic route is easy and rapid for preparing a variety of nanocomposites. The method avoids use of toxic chemicals, and the prepared nanocomposites can be used for biosensor, fuel cell, and biomedical applications.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of U.S. application Ser. No. 15/474,760,filed Mar. 30, 2017, which is a continuation-in-part of U.S. applicationSer. No. 14/666,307 filed Mar. 24, 2015.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to composites, and particularly to amethod for producing noble metal nanocomposites that have noble metalnanoparticles (MNP) embedded in a carbon-based substrate of grapheneoxide (GO) or carbon nanotubes (CNT).

2. Description of the Related Art

Noble metal nanoparticles have gained remarkable attention due to theirexcellent physical, chemical and biological properties. On the otherhand, carbon-based nano-materials, including graphene oxide (GO) sheetsand carbon nanotubes (CNT), are promising supporting materials for noblemetal nanoparticles to produce new nanocomposites that can be used in awide variety of applications because of their distinctive electronic,thermal, and mechanical properties. Currently, the search for syntheticroutes for embedding metal nanoparticles on carbon-based materials is arapidly growing research area in nanoscience and nanotechnology. So far,there have been a number of attempts to carry out a synthesis of noblemetal nanoparticles embedded graphene oxide and carbon nanotubes,including chemical reduction, electrochemical, thermal decomposition,ultraviolet and microwave irradiation. However, these methods usehazardous chemicals, high pressure, energy, and temperatures that leadto environmental pollution. Green synthesis is a most promising methodfor metal nanoparticles (MNPs) synthesis that is considered costeffective, simple, rapid, and eco-friendly, since it does not requiretoxic chemicals. We have developed a new synthetic route for synthesisof MNPs on GO/CNT. These synthesized samples can be used for biosensors,fuel cells, and biomedical applications.

Thus, a method for producing noble metal nanocomposites solving theaforementioned problems is desired.

SUMMARY OF THE INVENTION

The method for producing noble metal nanocomposites involves reducingnoble metal ions (Ag, Au and Pt) on graphene oxide (GO) or carbonnanotubes (CNT) by using Artocarpus integer (champedak) leaves extractas a reducing agent. As synthesized MNPs/GO and MNPs/CNT composites havebeen characterized using X-ray diffraction (XRD), transmission electronmicroscope (TEM) imaging, and energy dispersive X-ray spectroscopy(EDX). The TEM images of prepared materials showed that thenanocomposites were 1-30 nm in size with spherical nanoparticlesembedded on the surface of GO and CNT. This synthetic route is easy andrapid for preparing a variety of nanocomposites. The method avoids useof toxic chemicals, and the prepared nanocomposites can be used forbiosensor, fuel cell, and biomedical applications.

These and other features of the present invention will become readilyapparent upon further review of the following specification anddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a TEM image of a Pt-CNT nanocomposite sample prepared by amethod for producing noble metal nanocomposites according to the presentinvention.

FIG. 1B is a TEM image of the same Pt-CNT nanocomposite sample shown inFIG. 1A, but at higher magnification.

FIG. 1C is a TEM image of a Pt-GO nanocomposite sample prepared by amethod for producing noble metal nanocomposites according to the presentinvention.

FIG. 1D is a TEM image of the same Pt-GO nanocomposite sample shown inFIG. 1C, but at higher magnification.

FIG. 2A is an EDX spectrum of the Pt-CNT nanocomposite sample shown inFIGS. 1A and 1B.

FIG. 2B is an EDX spectrum of the Pt-GO nanocomposite sample shown inFIGS. 1C and 1D.

FIG. 3A is a TEM image of an Au-CNT nanocomposite sample prepared by amethod for producing noble metal nanocomposites according to the presentinvention.

FIG. 3B is a TEM image of the same Au-CNT nanocomposite sample shown inFIG. 3A, but at higher magnification.

FIG. 3C is a TEM image of an Au-GO nanocomposite sample prepared by amethod for producing noble metal nanocomposites according to the presentinvention.

FIG. 3D is a TEM image of the same Au-GO nanocomposite sample shown inFIG. 3C, but at higher magnification.

FIG. 4A is an EDX spectrum of the Au-CNT nanocomposite sample shown inFIGS. 3A and 3B.

FIG. 4B is an EDX spectrum of the Au-GO nanocomposite sample shown inFIGS. 3C and 3D.

FIG. 5A is a TEM image of an Ag-CNT nanocomposite sample prepared by amethod for producing noble metal nanocomposites according to the presentinvention.

FIG. 5B is a TEM image of the same Ag-CNT nanocomposite sample shown inFIG. 5A, but at higher magnification.

FIG. 5C is a TEM image of an Ag-GO nanocomposite sample prepared by amethod for producing noble metal nanocomposites according to the presentinvention.

FIG. 5D is a TEM image of the same Ag-GO nanocomposite sample shown inFIG. 5C, but at higher magnification.

FIG. 6A is an EDX spectrum of the Ag-CNT nanocomposite sample shown inFIGS. 5A and 5B.

FIG. 6B is an EDX spectrum of the Ag-GO nanocomposite sample shown inFIGS. 5C and 5D.

Similar reference characters denote corresponding features consistentlythroughout the attached drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The method for producing noble metal nanocomposites involves reducingnoble metal ions (Ag, Au and Pt) on graphene oxide (GO) or carbonnanotubes (CNT) by using Artocarpus integer (champedak) leaves extractas a reducing agent. As synthesized MNPs/GO and MNPs/CNT composites havebeen characterized using X-ray diffraction (XRD), transmission electronmicroscope (TEM) imaging, and energy dispersive X-ray spectroscopy(EDX). The TEM images of prepared materials showed that thenanocomposites were 2-20 nm in size with spherical nanoparticlesembedded on the surface of GO and CNT. This synthetic route is easy andrapid for preparing a variety of nanocomposites. The method avoids useof toxic chemicals, and the prepared nanocomposites can be used forbiosensor, fuel cell, and biomedical applications.

In the following examples, leaves of Artocarpus integer were collectedfrom the Kanyakumari Dist., Tamil Nadu (India). Graphite and CNT werepurchased from S.D.Fine, Inida and Sigma, USA respectively. Milli Qwater was used throughout the experiments.

Freshly harvested A. integer leaves were washed several times withdeionized water. About 10 g of leaves were finely chopped and stirred in200 ml of double-distilled water at 95° C. for 5 min and filtered usinga Whatman #1 filter paper to obtain the leaf extract. The filtrate wasused as the reducing agent.

Graphene oxide was synthesized from graphite by modified Hummers method.Briefly, 1.0 g graphite powder was dispersed in 24 mL concentrated H₂SO₄under stirring at 0° C. Subsequently, 3.0 g of KMnO₄ was added graduallyto the mixture and kept in an ice bath. The mixture was stirred for 30min. The mixture was diluted gradually with 45 mL Milli-Q water. Themixture was re-diluted with 140 mL Milli-Q water and treated withdrop-wise addition of 3% hydrogen peroxide. The color of the mixturechanged to yellow-brown during the drop-wise addition of H₂O₂. Themixture was filtered and washed with HCl solution (5%) and thenrepeatedly washed with water. Finally, the dark brown graphene oxide(GO) powder was obtained through drying at 50° C. in a vacuum oven.

Functionalized MWCNT (multi-wall carbon nanotubes) were prepared bybrutal oxidation using an H₂SO₄— HNO₃ mixture (3:1 v/v ratio). About 1 gof MWCNT was refluxed with 100 ml of the acid mixture at 120° C. for 6h. After cooling, the reaction mixture was diluted with 500 ml ofMilli-Q water and filtered through vacuum filtration. The obtainedproduct was washed several times with Milli-Q water until the acid wasremoved. The functionalized MWCNT were used for further experiments.

To obtain platinum nanocomposites, about 20 mg of either GO or thefunctionalized MWCNT was dispersed in 20 ml Milli-Q water undersonication for 30 minutes. About 5 ml of 1×10⁻² M H₂PtCl₆ solution wasadded drop-wise in GO or the functionalized MWCNT separately understirring. Following that, the mixture was kept at room temperature foraging and GO-Pt⁺ or MWCNT-Pt⁺ complex formation. Excess metal ions ofGO-Pt⁺ or MWCNT-Pt⁺ mixture were removed by centrifugation. Then 5 ml ofthe leaves broth (extract) was added to the obtained GO-metal complex orMWCNT-metal complex and mixed well. After 15 minutes incubation, thesamples were used for further physico-chemical characterization.

To obtain gold nanocomposites, about 20 mg GO or the functionalizedMWCNT was dispersed in 20 ml Milli-Q water under sonication for 30minutes. About 5 ml of 1×10⁻² M HAuCl₄ solution was added drop-wise inGO or the functionalized MWCNT separately under stirring. Followingthat, the mixture was kept at room temperature for aging and GO-Au⁺ orMWCNT-Au⁺ complex formation. Excess metal ions of the GO-Au⁺ or theMWCNT-Au⁺ mixture was removed by centrifugation. Then, about 5 ml of theleaves broth (extract) was added to the obtained GO-metal complex or theMWCNT-metal complex and mixed well. After 15 minutes incubation, thesamples were used for further physico-chemical characterization.

To obtain silver nanocomposite, about 20 mg GO or the functionalizedMWCNT was dispersed in 20 ml Milli-Q water under sonication for 30minutes. About 5 ml of 1×10⁻² M AgNO₃ solution was added drop-wise inthe GO or the functionalized MWCNT separately under stirring. Followingthat, the mixture was kept at room temperature for aging and GO-Ag⁺ orMWCNT-Ag⁺ complex formation. Excess metal ions of the GO-Ag⁺ or theMWCNT-Ag⁺ mixture were removed by centrifugation. Then, 5 ml of theleaves broth (extract) was added to the obtained GO-metal complex or theMWCNT-metal complex and mixed well. After 15 minutes incubation, thesamples were used for further physico-chemical characterization.

Chemical compositions of prepared noble metal nanocomposites werecharacterized by using Energy Dispersive X-ray analysis (EDAX or EDX).See FIGS. 2A, 2B, 4A, 4B, 6A and 6B. The crystalline nature of theprepared samples was analyzed using X-ray diffraction (XRD). The surfacemorphology, particle size and diameter of the prepared materials werecharacterized by using Transmission electron microscope (TEM) (JEOL,JEM2100, Japan). See FIGS. 1A, 1B, 1C, 1D, 3A, 3B, 3C, 3D, 5A, 5B, 5Cand 5D.

The crystalline nature of the platinum, gold, and silver nanocompositeswas confirmed by the X-ray diffraction analysis. The typical XRDpatterns of the prepared samples could be indexed to (1 1 1), (2 0 0),(2 2 0), and (3 1 1) planes of face-centered cubic bulk metalliccounterparts.

The morphology and particle size of the prepared platinum nanocompositeswere analyzed using transmission electron microscopy. FIGS. 1A-ID showTEM images of the platinum nanocomposites. The platinum nanoparticlesize varied between 1-3 nm. The TEM images suggested well dispersedplatinum particles on the graphene oxide and carbon nanotube substrates,respectively. The elemental profiles of the prepared nanocomposites wereanalyzed using TEM with an energy dispersive spectroscopy (EDX) setup.The EDX spectrum (FIG. 2A) for the Pt-CNT nanocomposite showed Pt, C,and Cu peaks, which suggested the presence of platinum nanoparticles onthe CNT. FIG. 2B exhibited the Pt, C, O, and Cu peaks, which indicatesthe presence of platinum nanoparticles on graphene oxide. The Cu peakscorrespond to the copper grid used for TEM analysis.

The morphology and particle size of the prepared gold nanocompositeswere analyzed using transmission electron microscopy. FIGS. 3A-3D showTEM images of the gold nanocomposites. Our results suggested that 10-20nm spherically shaped gold nanoparticles are uniformly formed on GO andCNT. The elemental profiles of the prepared nanocomposites were analyzedusing TEM with an energy dispersive spectroscopy (EDX) setup. The EDXspectrum (FIG. 4A) for the Au-CNT nanocomposite showed Au, C, and Cupeaks, which suggested the presence of gold nanoparticles on the CNT.FIG. 4B exhibited the Au, C, O, and Cu peaks, which indicates thepresence of gold nanoparticles (Au) on graphene oxide (C, O). The Cupeaks correspond to the copper grid used for TEM analysis.

The morphology and particle size of the prepared silver nanocompositeswere analyzed using transmission electron microscopy. FIGS. 5A-5D showTEM images of the silver nanocomposites. The TEM results confirmed that20-30 nm silver nanoparticles are present on the GO and CNT substrates.The elemental profiles of the prepared nanocomposites were analyzedusing TEM with an energy dispersive spectroscopy (EDX) setup. The EDXspectrum (FIG. 6A) for the Pt-GO nanocomposite showed Ag, C, and Cupeaks, which suggested the presence of silver nanoparticles on the CNT.FIG. 6B exhibited the Ag, C, O, and Cu peaks, which indicates thepresence of silver nanoparticles on graphene oxide. The Cu peakscorrespond to the copper grid used for TEM analysis.

It is to be understood that the present invention is not limited to theembodiments described above, but encompasses any and all embodimentswithin the scope of the following claims.

1-10. (canceled)
 11. A method for producing noble metal nanocomposites,comprising the steps of: preparing an aqueous solution of grapheneoxide; adding an aqueous solution of a salt of a noble metal to thesolution of the graphene oxide to form a complex of the graphene oxideand the noble metal ion in aqueous solution; and adding an extract ofArtocarpus integrifolia leaves to the aqueous solution of the noblemetal ion-graphene oxide complex in order to reduce the noble metal ion,thereby forming a composite of nanoparticles of the reduced noble metalembedded on the graphene oxide and having a particle size between 1 nmand 30 nm.
 12. A platinum-graphene oxide nanocomposite preparedaccording to the method of claim
 11. 13. (canceled)
 14. A gold-grapheneoxide nanocomposite prepared according to the method of claim
 11. 15.(canceled)
 16. A silver-graphene oxide nanocomposite prepared accordingto the method of claim
 11. 17. (canceled)
 18. The method for producingnoble metal nanocomposites according to claim 11, wherein the noblemetal is selected from the group consisting of platinum, gold, andsilver.
 19. The method for producing noble metal nanocompositesaccording to claim 11, wherein the noble metal is platinum and thenanoparticles of the reduced noble metal have a particle size between 1nm and 3 nm.
 20. The method for producing noble metal nanocompositesaccording to claim 11, wherein the noble metal is gold and thenanoparticles of the reduced noble metal have a particle size between 10nm and 20 nm.
 21. The method for producing noble metal nanocompositesaccording to claim 11, wherein the nanoparticles are substantiallyspherical.
 22. The method for producing noble metal nanocompositesaccording to claim 11, wherein the noble metal is silver and thenanoparticles of the reduced noble metal have a particle size between 20nm and 30 nm.